Venting overhead condenser responsive to pressure differential



Aug. 16, 1966 c. s. KELLEY 3,266,260

VENTING OVERHEAD CONDENSER RESPONSIVE TO PRESSURE DIFFERENTIAL Filed Oct. 25. 1965 0 Q m- E F lg D l CLCI w 22 8 2 H 5, 5 Q I o 2 EE 50 0 m v #0 (D (O o b I Z w 0 10 P 1 H 3 HQ CO q- 10 l (D J J w z "0 2 g u E .1 I m 5: q N if an L O N 2 3; o

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w N n l m INVENTOR. D m 3 c. s. KELLEY ATTORNEYS United States Patent 3,266,260 VENTING OVERHEAD CONDENSER RESPONSIVE TO PRESSURE DIFFERENTIAL Carl S. Kelley, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 23, 1963, Ser. No. 318,358 8 Claims. (Cl. 62-21) This invention relates to the fractionation of fluid materials. In one aspect this invention relates to a process for the fractionation of hydrocarbon mixtures. In another aspect the invention relates to a method for the separation of lighter from heavier components of a normally gaseous mixture. In still another aspect the invention relates to the separation of ethane and lighter hydrocarbons from a mixture containing substantially propane.

It is well known to fractionate crude petroleum which is a mixture of hydrocarbons which rangephysically and structurally over a wide range. Thus, by ordinary distillation methods, such as atmospheric distillation, crude oil may be separated into such products as gas, liquefied petroleum gases (LPG), gasoline, kerosene, gas oil and topped crude. Ordinary distillation methods are satisfactory for the separation of the light fractions such as gasoline, kerosene, and gas oil; however, topped crude or heavy residues, can not be separated into its fractions such as heavy gas oil and asphaltic residue using atmospheric distillation without cracking occurring. Therefore, vacuum distillation and/or solvent fractionation must be used on these heavier materials in order to recover therefrom the hydrocarbon fractions, including lubrication oil base stocks and asphalts.

A number of methods have been disclosed in the art for the separation of asphalt-free lubricating oil base stocks from an asphalt-containing oil, such as a topped crude oil. For example, the crude oil may be distilled at about atomspheric pressure to remove the lighter gas oils, kerosene-type distillates, gasoline, liquefied petroleum gases (liquefied propane and butane) and light gases including ethane and methane. Substantially no cracking occurs at the required temperatures and hence no degradation of the heavier lubricating oil components occurs. The residue from this atmospheric distillation, commonly called topped crude, is then subjected to vacuum distillation under conditions wherein substantially no cracking occurs, to produce distillates which are further treated (e.g. by phenol extraction and by dewaxing) to produce the lighter lubricating oil blending stocks. The vacuum reduced crude residue containing the asphalt and the heavier lubricating oil components is then extracted under pressure with liquid propane. The asphaltic material in the petroleum residue, being insoluble in light propane, remains undissolved whereas the oils present form a solution with the propane which is easily separable from the undesirable asphalt by ordinary decantation methods. The oily constituents dissolved in the propane are recovered by allowing the propane to distill oil under reduced pressures. The oils prepared by this method are substantially free of asphalt and are further treated (e.g. by phenol extraction and by dewaxing) to produce the heavier lubrication oil base stocks. The asphalt or flux oil is substantially free of lubricating oil base constituents, as these components are removed by the liquid propane.

However, in this socalled propane deasphalting method, a principal operating cost is the circulation of large quantities of propane through the high pressure extractor. In order to keep the expenses low it is necessary (1) to p'revent'overcooling or overheating of the propane (2) to keep the system vented to prevent accumulation of excess ethane and lighter components without excessive ice loss of propane and (3) have the unit under accurate control of temperature and flow conditions.

While the invention is particularly described with reference to the venting of ethane and lighter components from propane deasphating solvent, it is believed obvious the invention is applicable to the separation of light components from any multicomponent fluid which is separable by temperature and pressure regulation.

It is an object of the invention to provide method and apparatus for fractionating components of a multi-component mixture.

Yet another object of the invention is to provide method and apparatus for controlling the venting of light components from a mixture of heavy and light fluid components separable by adjustment of temperature and pressure.

Still another object of the invention is to provide improved method and apparatus for the separation of ethane and lighter components from a mixture containing substantially propane, ethane and lighter components.

These and other objects of the invention will be readily apparent to those skilled in the art from the accompanying disclosure, drawing and appended claims.

These objects are broadly accomplished by venting the ethane and lighter components containing equilibrium amounts of the heavier components from a confined zone,

condensing the heavier components from said vented material and introducing all the vented material into a second confined zone, recycling the condensate from second confined zone to the first confined zone, maintaining a pressure in said second confined zone less than that in said first zone and venting at least a portion of the gases in said second zone when the difierence in pressure decreases below a predetermined value.

In one embodiment the pressure differential is maintained by the difference in elevation between said first and second vessel, said second vessel having a higher elevation than said first vessel.

In another embodiment the condensate accumulated in the first zone is passed into a third zone maintained at an elevated temperature and pressure, a multi-component mixture substantially identical to that introduced into the first zone is introduced into the third zone at a temperature and pressure greater than that in the first Zone and a portion of the lighter components containing an equilibrium amount of the heavier components is withdrawn and reduced in pressure and passed to said first zone.

By the method of this invention the temperature of the recycle propane accumulator is controlled and the light components are bled only when necessary which. reduces the loss of propane product. In addition, since the invention is particularly adaptable to automatic operation no attention is required by an operator.

The invention is best described with reference to the attached drawing which shows a preferred embodiment of the invention wherein propane solvent from a propane deasphalting operation is treated for the removal of ethane and lighter components. The propane deasphalting operation will generally produce with its downstream steps a so-called low pressure propane and a so-called high pressure propane from the propane evaporators as it is understood by those familiar with this field. The low pressure propane generally has a temperature in the range of F. to 225 F. and a pressure in the range of 180 p.s.i.g. to 220 p.s.i.g.; and the high pressure propane has a temperature of 175 F. to 225 F. and a pressure of 450 p.s.i.g. to 600 p.s.i.g. The low pressure material containing substantially propane with small quantities (usually less than about 3 mol percent) of ethane and lighter components is introduced through conduits 2 and 4 and cooled in condenser 6 to a temperature in the range of about 90 F. to about 110 F. and a pressure in the range of about 180 p.s.i.g. to 210 p.s.i.g.

The cooled propane mixture is then passed through conduit 8 into the accumulator 10. Water (steam condensate from prior steam stripping) and the like is removed through settling leg 12 through conduits 14 and valve 16. Due to the pressure and temperature in the accumulator 10 a substantially pure propane stream can be withdrawn through conduit 18 from a lower portion of the accumulator. The upper portion of the accumulator 10 is vented through conduit 20 to provide a possible escape for ethane and lighter components along with an equilibrium quantity of propane. These components are passed through a restriction orifice 22 or any other suitable method for reducing the pressure to substantially that of the accumulator 30 as herein before described. The vented materials then passed through conduit 24, cooling heat exchange means 26, conduit 28, into the accumulator 30. This accumulator is maintained at a pressure slightly less than that of the pressure within the accumulating vessel 10. One suitable method for doing this is to elevate the accumulating vessel 30 at a distance above that of vessel 10. For example, a 7-foot elevation (liquid propane) will provide a pressure differential of 1.5 p.s.i. When the ethane and lighter components are at a minimum there will be no venting through conduit 40, valve 36, and conduit 38, and all of the liquid propane will be returned through conduit 32 to vessel 10. A minimum differential of pressure is maintained across the restriction orifice and the heat exchanger 26 by a differential pressure controller 42 which receives signals from pressure sensing means 40 and 39. The accumulating vessel 30 can be operated at a pressure in the range of about 120 p.s.i.g. to about 210 p.s.i.g. and a temperature in the range of about 80 F. to about 90 F. to provide a differential pressure of not less than about 1 p.s.i. and preferably in the range of about 1 p.s.i. to about 20 p.s.i. Due to the difference in elevation between vessel 30 and vessel 10, if there are no inert gases or noncondensibles such as ethane and lighter components, the propane stream being vented through conduit 20 from vessel 10 to vessel 30 will be condensed cornpletely, and the preselected minimum differential pressure will be maintained which keeps vent valve 336 closed. However, if the ethane and lighter components build up in the system the condenser 26 cannot condense all of these causing an increase in pressure in vessel 30 with a corresponding decrease in the differential pressure. The control valve 36 is actuated to be opened by this decreased differential pressure sensed by differential pressure controller 42 responsive to signals from pressure sensing means 39 and 40. This permits enough flow from vessel 30 through vent 38 to hold the preselected minimum differential pressure. When all of the ethane and lighter components and other inerts are vented the preselected minimum differential pressure is re-established which then permits the vent valve 36 to be closed.

Preferably, vessel 30 is maintained at an elevation of about feet to about 20 feet above vessel (however, any reasonable height above 5 feet, e.g. even 100 feet could be used) so as to maintain the pressure preselected minimum differential pressure of about 1 p.s.i. to about p.s.i. However, any suitable means can be provided for maintaining the pressure differential required.

When employing a system providing both high pressure and low pressure propane streams, it is advantageous to pass the liquid propane withdrawn from vessel 10 through conduit 18, pump 19, and line 21 through valve 84 and conduit 23 back into a third confined zone or accumulator 58. The flow of liquid propane from vessel 10 to vessel 58 is controlled by liquid level controller 82 adapted to actuate valve 84. The high pressure propaneccntaining stream also containing (usually less than about 3 mol percent) ethane and lighter components is intro- 4 duced from the high pressure evaporators through conduit 44 and 46 cooled in heat exchange means 48. The cooled propane is then passed through conduits 50, 52, mixing T 54 and conduit 56 into the accumulator 58. Control of the temperature of the incoming high pressure propane mixture is suitably controlled by by-passing cooling means 48 by diverting some of the propane through conduit 60, valve 62, conduit 64, mixing T 54 and conduit 56 into vessel .78. For example, if the pressure is too low pressure recorder controller 66 receives a signal from pressure sensing means 68 and actuates valve 62 so as to further open and allow an increase in the quantity which will by-pass the cooling means. A finer control is provided by a temperature controller 72 responsive to a signal from temperature sensing means 70 so as to reset the pressure recorder controller 66. By the use of the pressure controller 66 on vessel 58 reset by the temperature controller 72 it is possible to hold a. very constant temperature on the liquid propane in spite of the variation in the cold propane from vessel 10 due to changes in cooling water and Weather. Liquid propane is withdrawn from vessel 58 through conduit 74, pump 76 and conduit 78 and passed back to the high pressure propane deasphalting operation.

A vent is provided in the upper portion of the vessel 58 to provide for a bleed of a very small amount, for example 0.1 to 0.2 percent of the propane circulation through the system. The flow is controlled by a restriction orifice 88. The vented stream passes through conduit and joins the incoming low pres-sure stream 2. The restriction orifice 88 permits the removal of ethane and lighter components keeping the cooler 48 operating more efli-- ciently.

In a specific embodiment of the invention low pressure propane at a pressure of 200 p.s.i.g. and a temperature of 210 F. and containing 2.4 mol percent of ethane and lighter components is passed to conduit 2 into vessel 10 which is maintained at F. and 193 p.s.i.g. Vessel 30 has a liquid propane head of 7 feet with respect to vessel 10 to provide a pressure differential of 1.5 p.s.i.

or a pressure of 191.5 p.s.i.g. in vessel 30. When the pressure differential, as determined by pressure sensing means 39 and 40, decreases below 1.5 p.s.i., valve 36 is actuated by pressure controller 42 to vent the ethane and lighter components. Propane containing ethane and lighter components from the high pressure evaporators is introduced at 190 F. and 410 p.s.i.g. through conduit 40 into vessel 58 which is maintained at F. and 400 p.s.i.g. This is combined with propane withdrawn from vessel 10 at 100 F. Propane is withdrawn from vessel 58 at 160 F. and passed to the high pressure deasphalting contactor. Restriction orifice 88 permits the bleeding of ethane and lighter components from vessel 58. This quantity is about 0.2 volume percent of the propane charged to vessel 58. A better understanding of the embodiment is obtainable from the following flow tabulation.

FLOW TABULATION Stream number Mols./hr. 2 100 44 200 78 a 297 38 '3 90 (approX.) 0.6 28 97.6

1 As required by system to maintain preselected minimum AP of 1.5 p.s.i. between vessel 10 and vessel 30 not a continuous flow, but an average over an extended period of operation.

While certain examples, structures, composition and process steps have been described for purposes of illustrations the invention is not limited to these. Variation and modification within the scope of the disclosure and in the claims can readily be effected by those skilled in the art.

I claim:

1. Apparatus comprising, in combination, a first vessel, a first and second inlet conduit to said first vessel, a first outlet conduit in a lower portion of said vessel, a second outlet conduit in an upper portion of said vessel in communication with a second vessel, a cooling means disposed so as to cool at least a portion of said second outlet conduit, a third outlet conduit in communication with the lower portion of said second vessel and said first vessel, a vent conduit in an upper portion of said second vessel, a valve means in said vent conduit, means for providing a pressure in said first vessel greater than the pressure in said second vessel, pressure sensing means disposed so as to determine the difference in pressure in said first and second vessels, and control means for actuating said valve means responsive to a signal from said pressure sensing means.

2. Apparatus for venting light gases from heavier gases comprising, in combination, a first vessel, a first inlet conduit thereto for introducing a mixture of normally gaseous components, a cooling means disposed in said feed inlet means for cooling said mixture of gaseous components to condense substantially all of the heavier components, a first outlet conduit in a lower portion of said first vessel for withdrawing liquid product, a second outlet in an upper portion of said first vessel for venting the lighter components in equilibrium with the heavier components, said second outlet being in communication with a second vessel which is elevated in relation to the first vessel so as to provide a predetermined difference in pressure between the interiors of said first and second vessels, a restriction in said second outlet for reducing the pressure, a cooling means disposed downstream from said restriction for cooling said second outlet to condense the heavier components therein, a third outlet conduit in communication with the lower portion of said second vessel and an upper portion of said first vessel, a vent conduit in an upper portion of said second vessel, valve means in said vent conduit, measuring means for determining the difference in pressure between the interiors of said first and second vessels and control means connected to said valve means responsive to a signal from said measuring means so that when the differential pressure between said first vessel and said second vessel decreases below the predetermined level the valve means is opened and vice versa.

3. The apparatus of claim 2 wherein said first outlet is in communication with a third vessel, said third vessel having a third inlet for introducing normally gaseous components thereto, a fourth outlet from said third vessel for withdrawing products, means for maintaining an elevated pressure in said third vessel, a second venting conduit in communication with the upper portion of said third vessel and the upper portion of said first vessel and a second restriction in said second venting conduit.

4. A method for fractionating gasifiable components of a multi-component mixture comprising introducing said mixture into a first confined zone, maintaining the pressure and temperature therein sufficient to condense substantially all the heavier components of said mixture, withdrawing said condensed heavier liquid therefrom, venting the gaseous portion containing equilibrium amounts of said heavier components from an upper portion of said zone, condensing the heavier components of said vented material and introducing all of said vented material into a second confined zone, recycling the con densate from said second confined zone to said first confined zone, maintaining a pressure in said second confined zone less than the pressure in said first confined zone and venting at least a portion of the gases in said second zone when the differences in pressure between said first confined zone and said second confined zone decreases below a predetermined value.

5. The method of claim 4 wherein the pressure differential is maintained by a diiference in elevation between said first and second vessel, said second vessel having a higher elevation than said first vessel.

6. The process of claim 4 wherein the liquid components withdrawn from said first zone is passed into a third confined zone maintained at elevated temperature and pressure, a multi-component mixture substantially identical to that introduced into said first zone at temperature and pressure greater than that introduced into said first zone is introduced into said third zone, the liquid heavier components are withdrawn from said third zone, a portion of the lighter components containing equilibrium amounts of the heavier components is withdrawn from said third zone, reduced in pressure and passed to said first confined zone.

7. A method for removing ethane and lighter components from a predominantly propane mixture comprising introducing said mixture into a first confined zone maintained at a pressure in the range of 180 to 220 p.s.i.g. and a temperature in the range of 175 to 225 F. to condense substantially all of the propane, withdrawing the liquid propane from a lower portion of said first zone, venting the ethane and lighter components containing equilibrium amounts of propane from an upper portion of said first zone, reducing the pressure on said vented materials to 180 to 210 p.s.i.g., condensing substantially all the propane in said vented materials by cooling to a temperature in the range of to R, introducing the cooled vented material to a second confined zone maintained at a temperature of 90 to 110 F. and a pressure of 180 to 210 p.s.i.g., said pressure being 1 to 20 p.s.i.g. less than the pressure in said first zone, recycling the condensate from said second zone to said first zone, and venting at least a portion of the ethane and lighter components from the upper portion of said second zone when the difference in pressure between said first and said second zone decreases below the above value due to an increase in the amount of ethane and lighter components in said second zone.

8. The process of claim 7 wherein the liquid propane withdrawn from said first zone is passed into a third confined zone maintained at elevated temperature and pressure, a propane containing mixture of propane, ethane, and lighter components is introduced into said third confined zone at a temperature and pressure greater than that introduced into said first zone, the liquid propane is withdrawn from said third zone and a portion of the ethane and lighter components containing equilibrium amounts of the propane is withdrawn from said third zone and reduced in pressure and passed to said first confined zone.

References Cited by the Examiner UNITED STATES PATENTS 2,601,009 6/ 1952 Swearingen.

2,619,814 12/1952 Kniel 62-28 X 2,664,719 1/1954 Rice 62-14 X 2,890,156 6/1959 Vantrain 202- 2,915,462 12/1959 Salmon 196-432 X 2,939,293 7/1960 Green 62-21 X 3,165,454 1/1965 Wienecke 196132 X NORMAN YUDKOFF, Primary Examiner. V. W. PRETKA, I. JOHNSON, Assistant Examiners. 

1. APPARATUS COMPRISING, IN COMBINATION, A FIRST VESSEL, A FIRST AND SECOND INLET CONDUIT TO SAID FIRST VESSEL, A FIRST OUTLET CONDUIT IN A LOWER PORTION OF SAID VESSEL, A SECOND OUTLET CONDUIT IN AN UPPER PORTION OF SAID VESSEL IN COMMUNICATION WITH A SECOND VESSEL, A COOLING MEANS DISPOSED SO AS TO COOL AT LEAST A PORTION OF SAID SECOND OUTLET CONDUIT, A THIRD OUTLET CONDUIT IN COMMUNICATION WITH THE LOWER PORTION OF SAID SECOND VESSEL AND SAID FIRST VESSEL, A VENT CONDUIT IN AN UPPER PORTION OF SAID SECOND VESSEL, A VALVE MEANS IN SAID VENT CONDUIT, MEANS FOR PROVIDING A PRESSURE IN SAID FIRST VESSEL GREATER THAN THE PRESSURE IN SAID SECOND VESSEL, PRESSURE SENSING MEANS DISPOSED SO AS TO DETERMINE THE DIFFERENCE IN PRESSURE IN SAID FIRST AND SECOND VESSELS, AND CONTROL MEANS FOR ACTUATING SAID VALVE MEANS RESPONSIVE TO A SIGNAL FROM SAID PRESSURE SENSING MEANS. 